TITLE:   GCN CIRCULAR
NUMBER:  37558
SUBJECT: GRB 240918B: Fermi GBM Detection
DATE:    24/09/19 15:47:35 GMT
FROM:    rachel.hamburg@ijclab.in2p3.fr

The Fermi GBM team reports the detection of a likely LONG GRB.

At approximately 20:56:58 UT on 18 Sep 2024, the Fermi Gamma-ray Burst Monitor (GBM)
detected GRB 240918B, which was observed about 107 s after GBM triggered on
GRB 240918A (trigger 748385716/240918872) (Fermi GBM Team 2024; GCN 37549).
Due to the GBM trigger buffer of 10 min, the GBM did not trigger on this GRB.

The on-ground calculated location, using the Fermi GBM trigger data from 107.52 s
to 115.71 s after trigger time, is RA = 142.54, Dec = -17.36 (J2000 degrees,
equivalent to J2000 9h 30m, -17d 36'), with a statistical uncertainty of 2.03 degrees.

The angle from the Fermi LAT boresight is 64 degrees.

The GBM Targeted Search [1], the most sensitive, coherent search for GRB-like signals,
was also used to identify GRB-like emission around the time of GRB 240918B. This search
finds a multi-peaked emission episode on timescales up to 4.096 s and showing a 
localization consistent with the on-ground location. The brightest peak (at 20:57:01 UT)
was found to be the most significant (FAR = 5.4e-06 Hz) on the 0.512 s timescale and 
best fit with a "normal" GRB spectrum as described in [1]."

[1] Goldstein et al. 2019 arXiv:1903.12597